I've inhaled commercial helium (who hasn't?) and lived with no noticeable repercussions... Straight up hydrogen? Not sure.

None of them are toxic, but hydrogen is explosive and both are asphixiants. 1) "Hydrogen poses a number of hazards to human safety, from potential detonations and fires when mixed with air to being an asphyxant in its pure, oxygen-free form. In addition, liquid hydrogen is a cryogen and presents dangers (such as frostbite) associated with very cold liquids. Hydrogen dissolves in some metals, and, in addition to leaking out, may have adverse effects on them, such as hydrogen embrittlement. Hydrogen gas leaking into external air may spontaneously ignite. However, hydrogen fire, while being extremely hot, is almost invisible, and thus can lead to accidental burns. Even interpreting the hydrogen data (including safety data) is confounded by a number of phenomena. Many physical and chemical properties of hydrogen depend on the parahydrogen/orthohydrogen ratio (it often takes days or weeks at a given temperature to reach the equilibrium ratio, for which the data is usually given). Hydrogen detonation parameters, such as critical detonation pressure and temperature, strongly depend on the container geometry." Source and further information: http://en.wikipedia.org/wiki/Hydrogen#Safety_and_precautions 2) "Helium (He) is a colorless, odorless, tasteless, non-toxic, inert monatomic chemical element that heads the noble gas series in the periodic table and whose atomic number is 2." "The voice of a person who has inhaled helium temporarily sounds high-pitched. This is because the speed of sound in helium is nearly three times the speed of sound in air. Because the fundamental frequency of a gas-filled cavity is proportional to the speed of sound in the gas, when helium is inhaled there is a corresponding increase in the resonant frequencies of the vocal tract. (The opposite effect, lowering frequencies, can be obtained by inhaling sulfur hexafluoride) Inhaling helium, e.g. to produce the vocal effect, can be dangerous if done to excess since helium is a simple asphyxiant, thus it displaces oxygen needed for normal respiration. Death by asphyxiation will result within minutes if pure helium is breathed continuously. In mammals (with the notable exceptions of seals and many burrowing animals) the breathing reflex is triggered by excess of carbon dioxide rather than lack of oxygen, so asphyxiation by helium progresses without the victim experiencing air hunger. Inhaling helium directly from pressurized cylinders is extremely dangerous as the high flow rate can result in barotrauma, fatally rupturing lung tissue. Neutral helium at standard conditions is non-toxic, plays no biological role and is found in trace amounts in human blood. At high pressures (more than about 20 atm or two MPa), a mixture of helium and oxygen (heliox) can lead to high pressure nervous syndrome, a sort of reverse-anesthetic effect; adding a small amount of nitrogen to the mixture can alleviate the problem. Containers of helium gas at 5 to 10 K should be handled as if they contain liquid helium due to the rapid and significant thermal expansion that occurs when helium gas at less than 10 K is warmed to room temperature." Source and further information: http://en.wikipedia.org/wiki/Helium#Biological_effects 3) "Hydrogen is not toxic but can act as a simple asphyxiant by displacing or diluting atmospheric air to the point where the oxygen content cannot support life. Unconsciousness without any warning symptoms can occur from inhaling pure hydrogen or air that contains more than 20 Vol% hydrogen. However the lower explosion limit – 4 Vol% hydrogen in air – is reached before the asphyxiant hazard level is achieved. Therefore the fire hazard of hydrogen far exceeds the asphyxiation hazard. Liquid hydrogen and the cold gas evolving from the liquid can produce severe cryogenic burns upon contact with the skin and other tissues. The eyes can be injured even by short exposure to the cold gas or splashed liquid. Contact between unprotected parts of the body with uninsulated installation containing liquid hydrogen can cause the flesh to stick and tear when an attempt is made to withdraw." "None of the mentioned gases is toxic or narcotic. Nitrogen, argon, helium and hydrogen have no physiological effect. When these gases are inhaled together with sufficient oxygen the health is not endangered. But these gases don´t support live. When they are inhaled without sufficient oxygen the risk of asphyxiation arises. Note: Asphyxiation is not due to any effect of the asphyxiant gas but it is caused exclusively by the missing oxygen. For asphyxiant gases – contrary to the toxic gases – there are no figures of admissible concentration at the working place. The only essential gas for human life is oxygen. Without sufficient oxygen human beings can survive for maximum three minutes." Source and further information: http://www.storhy.net/train-in/PDF-TI/10_Linde-Notes.PDF

No, but I would rather inhale the air around me than some isolated gas. "Cough, cough! Ugh." :)

Too much helium can give you a severe headache. If hydrogen is to the point to where you can inhale it, it would freeze your mouth and lungs. So I would say both.

Neither Hydrogen nor Helium are poisonous to inhale. They are both found naturally occurring (both less than 1%) in the air around us so we are all breathing both gasses all the time. It is safe to breath the helium out of a balloon with no ill effects. Helium is used in some SCUBA equipment to reduce the need to use so much nitrogen at levels of about 33%. The only danger they have is if either of them were present in large enough quantities to reduce the amount of oxygen we are breathing to the point where we would suffocate. And the only time we would be frozen by either gas is if they were cool to a point at which they would freeze us. It is possible for the very air we breath to be cooled to the point where it would freeze our lungs. This can happen naturally in places like the Arctic.

i am new to this site am nearly 17 but i do chem at school in australia.... i must say to what everyone else has posted that... well they're kinda dumb u see the elements do occur naturally but inhaling concentrated amounts means that your not getting the oxygen your brain needs. so while it's not poisonous a high enough concentration in a room will knock you out then starve your brain of oxygen slowly turning your processing abilities to mush and your coordination to crap.... possibly to the point of you needing to have your butt wiped for you one day